NDI Audio Input Bug - volume lowered by around 3db

[andrewnielson]

It seems that sending audio via NDI into OBS lowers the volume by around 3db (when compared with other applications). This might not be a big deal for some (and of course you can adjust the volume in OBS though this may introduce noise). I tested this by playing a 1kHz Sine Wave from our Behringer x32 mixer connected via USB to our computer and then fed it via NDI (using ProPresenter) to OBS. I then compared this to feeding it directly to OBS (still via USB just not via ProPresenter).

Here's what the audio looked like in ProPresenter (-4db) before it was sent out using NDI:

Here's what the leve looked like in OBS when fed via NDI from ProPresenter (note the level is -8db):

Here's what the same NDI feed looked like when monitored with NDI Studio (note the level is higher than -6db at around -5db):

and for comparison, here's what it looked like being fed directly from the mixer (still via USB) to OBS (note the level is -5db):

From the above testing and screenshots, it would appear that the NDI audio input in OBS is lowering the volume by around 3db.
The testing was done on OBS Studio 27.0.1 running on Windows 10 and using ProPresenter 7.5.3. Log file is here: https://obsproject.com/logs/Tw4fmME_6Ye_EP3N

 

[konsolenritter]

In OBS the peak seems to be -5dB, the rms (avg) level -8dB, what fits fine for a sinusoidal test.
Thru the propresenter it seems -8dB peak (average then -11dB), so you seem right on that.

The screenshot of the NDI monitor i can't read/interpret. Is it the peak or rms level which is shown? This kind of level metering is dreadful... ;)

Are the two channels coming thru the propresenter true stereo already into its (propresenter's) mixing engine? Otherwise (if handled as two mono sources mixed and panned into an common stereo bus) the 3dB difference might be correct. That is often the case with software thinking of audio inputs just as (mono) mic sources.

 

[andrewnielson]

I can't seem to find any documentation to indicate if NDI monitor is rms or peak. :(

The two channels coming from the mixer are true stereo from the mixer, to the sound card and to ProPresenter and OBS. So it's true stereo the whole way through.